1. Field of the Invention
The present invention relates to a wireless communication terminal used in a wireless communication system that supports broadcast/multicast services.
Priority is claimed on Japanese Patent Application No. 2005-159600, filed May 31, 2005, the content of which is incorporated herein by reference.
2. Description of the Related Art
In wireless communication in which wireless communication terminals move freely within an area in which the wireless communication is provided, a technique called “handoff” is used to maintain the communication when a wireless communication terminal goes out of an area covered by one wireless base station and moves to an area of an adjacent different wireless base station or another sector. One method for achieving such a handoff is a method in which a signal for measurement is sent by respective wireless base stations with certain radio field intensity for measurement of the radio field intensity and a wireless communication terminal receives the signals and switches to another wireless base station. This method is an important technique for maintaining a communication channel since the status of reception of the wireless channel is maintained in a certain condition. For example, details of handoffs in accordance with the IS95 scheme are described in many documents, such as Japanese Unexamined Patent Application, First Publication No. 2003-189346.
On the other hand, from the viewpoint of effective utilization of wireless channels, a new service for wireless communication called Broadcast Multicast Service (BCMCS) has been proposed. This service is one type of broadcast service in which a plurality of wireless communication apparatuses simultaneously share a single communication channel called a “broadcast channel” for receiving information by the plurality of wireless communication apparatuses from the one channel providing a service of a broadcast type (i.e., a broadcast service). The service enables each wireless base station to broadcast common information to wireless communication terminals within their respective areas. Furthermore, since a respective channel is not required to be established by each wireless communication terminal, it becomes possible to distribute a large volume of data, such as news or movies, thereby improving utilization of the wireless channel. Furthermore, since it is possible to control each base station, unlike in a general wide-area broadcast service, distribution of information that is more closely related to the local area is made possible.
The procedure for information distribution of BCMCS will be described briefly. A wireless base station sends notification information relating to services that the wireless base station can offer to all wireless communication terminals within its wireless area. A wireless communication terminal receives the information and starts to receive a service it desires to receive by registering identification information that specifies the service with the wireless base station. The wireless base station receives the registering information from the wireless communication terminal and starts to provide the service if the service desired by the wireless communication terminal is not being provided at present (the information content is not being provided). The BCMCS stops provision of information content when no user is using the service from the viewpoint of effective utilization of wireless resources, and frees the communication channel used for the BCMCS so that the channel can be used as a general channel.
However, this method has the shortcoming that when a wireless communication apparatus using the BCMCS moves within the communication area of the wireless base station and hands off to another wireless area (for example, a cell or a sector). With the conventional wireless communication technologies, it is possible to maintain the wireless communication channel. However, the wireless base station to which a wireless communication terminal is currently connected and is providing the service does not notify whether or not the broadcast service is currently being provided. The statuses of services provided by a handoff destination base station, such what types of service is being provided, are unknown. As a result, the service provided through the BCMCS cannot be maintained.